The present invention relates to a method for the isolation of a water soluble native xcex2-glucan composition from oats, to the corresponding composition as such, and to products prepared from this composition.
Water soluble native xcex2-glucan is of major nutritional interest. It is the chemical constituent of xe2x80x98soluble dietary fiberxe2x80x99, SDF, considered to be responsible for the association between oats products and reduced risk for coronary heart disease. In this context the term xe2x80x98nativexe2x80x99 indicates that the carbohydrate has not been degraded enzymatically to a substantial extent during its isolation. A variety of health food products rich in SDF are currently on the market.
Barley and oats are rich in SDF. Oats SDF is documented as being particularly healthy.
A method for making a SDF composition from oats is disclosed in U.S. Pat. No. 4,996,063 (Inglett). The method of Inglett comprises gelatinizing a milled oat substrate prior to treating it with an xcex1-amylase which may yield substantial amounts of glucose. From the hydrolyzed mixture, an aqueous SDF fraction is recovered by separating water insoluble material. The usefulness of the xcex2-glucan product produced by the method of U.S. Pat. No. 4,996,063 as a food additive is however diminished by its high glucose content. A high content of glucose promotes the formation of undesired, that is, colored and bitter products on heating in the presence of amino acids (Maillard reaction). Moreover the Maillard reaction preferentially consumes lysine which is an amino acid essential to man. In many aplications a high glucose content is a drawback because of the sweetness of glucose.
In the context of producing and further handling SDF, it is important to prevent the action of xcex2-glucanase possibly present to avoid xcex2-glucan degradation which would ensue in loss of nutritional value. It is also important to provide the xcex2-glucan product essentially free of xcex2-glucanase.
The production of pure and stable SDF from oats is hampered by its rather high content of fat, proteins and, in particular, xcex2-glucanase.
It is an object of the present invention to provide a method of the aforementioned kind enabling the production of a stable, high yield xcex2-glucan composition from oats.
It is another object of the invention to provide a method for the production of a stable, high yield, water soluble xcex2-glucan composition from oats which has low sweetness and high temperature stability under conditions of food preparation and food processing.
It is a further object of the present invention to provide corresponding compositions and products prepared from them.
According to the invention is disclosed a method for producing, from an oats flour fraction, a water soluble xcex2-glucan composition having a high xcex2-glucan/glucose weight ratio, preferably a ratio of 15:1 or more, the method comprising the use of xcex2-amylase in an amount sufficient to transform more than 50% by weight, preferably more than 65% by weight, of the starch contained in the oats flour fraction to maltose. In addition substantial amounts of water soluble oligosaccharides are formed.
It is preferred for the method according to the invention to comprise, in addition to the use of xcex2-amylase, the use of pullulanase which xe2x80x98promotesxe2x80x99 the action of xcex2-amylase. Pullulanase is a starch debranching enzyme which also aids saccharification to disaccharides and maltose as the dominating monosaccharide while not promoting the formation of glucose.
According to an advantageous aspect of the invention, it is preferred for the method according to the invention to additionally comprise the use of protease. This is particularly advantageous if a purification of the xcex2-glucan composition of the invention to increase its content of water soluble xcex2-glucan is contemplated.
According to another advantageous aspect of the invention, it is preferred for the method of the invention to comprise the use of (in terms of enzymatic activity in relation to xcex2-amylase) xcex1-amylase in an amount capable to accelerate the starch degradation process but not to form substantial amounts of glucose. It is preferred to add from 0 to 10%, more preferred from 1 to 5%, of xcex1-amylase in terms of enzymatic activity relative to xcex2-amylase. The person skilled in the art will realize that the amount of xcex1-amylase needed for this end will vary according to reaction conditions (time, temperature, etc.) but can be easily determined by simple experimentation.
In particular, the method of the invention comprises the following steps:
selecting an oats variety rich in xcex2-glucan and, optionally, low in fat;
producing oats flour by dry-milling of said oats variety;
selecting an oats flour fraction rich in xcex2-glucan by sieving or other particle size/weight discriminating means;
adding to an aqueous medium the flour fraction which had been heat-treated as such or prepared from a heat treated oats variety or from heat-treated oats flour, xcex2-amylase and, optionally, pullulanase;
adding to an aqueous medium the thus treated flour fraction, xcex2-amylase and, optionally, pulullanase;
heating the thus produced suspension at a temperature above 30xc2x0 C. for a time period sufficient to substantially degrade starch;
inactivating added enzymes by further heating of the suspension and/or by other means;
forming a water soluble xcex2-glucan composition by removing water insoluble material;
optionally, concentrating and/or drying said xcex2-glucan composition.
It is preferred for the temperature at which the suspension is heated to degrade most of the starch and proteins to be from 52xc2x0 C. to 65xc2x0 C., in particular about 55xc2x0 C.
The temperature at which the suspension is heated to inactivate the added enzymes is preferably from about 80xc2x0 C. to about 95xc2x0 C.
It is preferred to form the water soluble xcex2-glucan composition by removing water insoluble material by centrifugation and/or filtration.
The xcex2-glucan composition of the invention may be used in form of its aqueous solution which, at higher concentrations, turns into a gel at room temperature, or in form of a powder obtained by, for instance, freeze or spray drying of aqueous solutions of the xcex2-glucan composition.
The xcex2-glucan composition of the invention can be used as a food additive, for instance as an additive of soft drinks and beer, the latter use being particularly preferred.
According to an advantageous aspect, the xcex2-glucan composition of the invention can be treated with a protease, in particular Alkalase(copyright), to degrade proteins to peptides and amino acids. This is particularly advantageous if removal of low-molecular weight compounds, for instance of compounds having a molecular weight of below 200, is contemplated. Apropriate methods for removal of low-molecular weight constituents include ultra-filtration, reverse osmosis, and gel filtration. It is also within the scope of the invention to add such enzymes prior or during the formation of the xcex2-glucan composition of the invention, for instance during the starch degradation step of the method of the invention.
The present invention also discloses food products enriched with the xcex2-glucan product of the invention. Enriched liquid products include fruit juices, beer, mash, milk and fermented liquid and semi-liquid dairy products, milk and cream substitutes, soft drinks, syrups, liquid honey, etc.
The xcex2-glucan product of the invention may also be used as a gelling additive in various food products. The freeze dried product is particularly suited as additive to solid or essentially solid food products, like bread, biscuits, chips, etc.
Further advantages of the invention are disclosed in the claims and will also be evident from a preferred, not limiting embodiment of the invention described in the following in greater detail by reference to a single Figure showing a chart illustrating the process the invention.